e-Golf battery upgrade: How does an EV know the size of battery it has installed?

[MrFlibble]

Hello - I'm new to this forum - hoping to learn and give back findings from my work.

For me, the VW Golf 7 is the perfect small car. The e-Golf improves on that, save for the relatively short range by modern standards.
I've developed a new obsession with the concept of upgrading the capacity of the e-Golf using new cells.

My initial approach is based on the concept that the e-Golf battery modules break down into PHEV2 form factor cells: 148 x 91 x 26.5 mm
https://pushevs.com/2020/07/03/modern-p ... ery-cells/

This would involve obtaining cells such as these:
https://www.evlithium.com/catl-battery- ... ttery.html
https://meddore.en.made-in-china.com/pr ... oters.html

If we disregard (for the moment!) the physical process of breaking down the pack and modules to get to the cells, replacing with higher capacity cells, reassembling the modules and putting the whole thing back together into the car...

Will the car throw faults now that it has higher capacity cells installed?
Since we have not changed the voltage of any of the cells, how would it even 'know' that the capacity has increased?

Readout from OBD11 shows something knows the capacity somehow - it would have to of course, so it can calculate range based on mi/kWh.
I assume that somewhere in the battery pack, in a BMS or other control module associated with the pack, there is a communication to the car that says 'I am a 35.8 kWh battery pack' and this won't change unless we tell it to: we've performed a 'dumb' swap.

So, in our thought experiment, we now have a car with 58 kWh that 'thinks' it has about 36 kWh.
Does the controller start to figure out over time that the voltage drops more slowly as charge is consumed - so the capacity must be greater?
Does it not, and so any range estimation is thrown off e.g., it reads 120 miles but this drops by 1 for every 1.6 miles driven?
Is it going to get 'confused' when charging and stop when it thinks 36 kWh should be in there, or is it more likely to charge until full 58 kWh by sensing flow of current vs voltage?
The potential for incorrect range readout doesn't bother me so much, but issues with proper charging would naturally be a problem.

VW did upgrade from 24 to 36 kWh with their 2017 facelift from mk 7 to 7.5, so perhaps it is possible to compare the information coming from the battery on both models to see where the capacity figure is stored, whether it can be edited or is on a ROM somewhere.

I get the feeling that, ultimately, I'm just going to have to try it and see in order to answer these questions with any certainty, but I wanted to understand any obvious pre-existing knowledge / pitfalls before jumping down the rabbit-hole (and potentially bricking a car... 'cheap' used e-Golfs are 8 to 10 kGBP as of 2024)

Lots of advice online appears to be 'jUsT bUy a nEw cAr' but I hope this is the right place where the spirit of this type of project and my intent is understood!

[dnoermann]

Hallo
I did not check your alternative Battery Cells.
I am preparing to Convert my T5.2 to E using E-Golf and E-Up Parts.
So i started in gathering Data.
I am doing Reverse engeneering VW ECU´s for some Years ....

Regarding your Capacy Change.
I guess the BMS is responsible for Broadcasting the Battery Chargelevel onto the Hybrind CAN Bus inside E-Golf.
Have a look at a VCDS auto Scan, see here https://forums.ross-tech.com/index.php?threads/22636/

Address 8C: Hybrid Battery (J840) Labels: None
Part No SW: 5GE 915 225 B HW: 5GE 915 225 B

That is the BMS Part which is connected yo HybirdCAN (resides inside the Battery)
And that one does have 8 Sub Components (Cell module: control modules) probably connected Via Lin Bus to the BMS

Since you own ODB11 you can look in the meassure Channels from 8C i would bed that you get all Battery Related information from there.

The Max Enery for shure is stored in a Value Saved inside the BMS or the Cell Modules, probably its part of the Dataset, thats Changeable Configuration Data in the VW World.
We could try comparing Datasets (XML Format) form the Pre 2020 E-Golf to the 2020, but for that we need to get hands on those Datasets ....

ODB11 is nice but i would suggedt getting VCDS, too, for future.

Anyhow simple change the Cells and see what happens.

As soon as i got my hand on a Cheep Crashed VW E-UP i will report back when i started reversing and got some results.
Greetings
Dennis

[MrFlibble]

Thanks - yes, I definitely see VCDS in my future!
Can VCDS extract the XML dataset you refer to, or is there another tool for that? ODIS perhaps?
I will look to get access to both e-Golf models once I know how to extract datasets, or perhaps someone here will already have them and can share.

Have a look at a VCDS auto Scan, see here https://forums.ross-tech.com/index.php?threads/22636/

The link you posted has some interesting info:

Address 8C: Hybrid Battery (J840) Labels: None
Part No SW: 5GE 915 225 B HW: 5GE 915 225 B
Component: K8C 005 0400
Serial number: 03012001013888
Coding: 000000000000000000000000000000000000000000000000000000000000
Shop #: WSC 00000 000 00000
ASAM Dataset: EV_BECM08820215GE915225B 001004
ROD: EV_BECM08820215GE915225B.rod
VCID: 3B2331C623E69683460-806E

Perhaps one of the numbers in there is interpreted as the installed capacity?

It seems that the SX6 unit of the e-Crafter/e-Golf battery pack has the J840 and J497 modules inside:
https://www.vag-technique.fr/ext_files/ ... rafter.pdf
I will be looking to obtain these units from both pre- and post- 2017 models of e-Golf to examine.

Since you own ODB11 you can look in the meassure Channels from 8C i would bed that you get all Battery Related information from there.

I currently have a Golf GTE, so I can see some data from the hybrid battery pack on 8C with OBD11 - I can get a capacity readout but not any obvious option to edit it.
The GTE also has an SX6 unit according to the self study guide for it:
https://www.stuartdalby.co.uk/vw_gte/SS ... lf_GTE.pdf

Perhaps also getting the units/datasets from this and the Passat GTE for a total of 4 different capacity datasets would be better for a comparison?:
- Golf GTE: 8.7 kWh
- Passat GTE: 13 kWh
- e-Golf pre-2017: 24.2 kWh
- e-Golf post-2017: 35.8 kWh

With your knowledge on reverse engineering of ECUs, is it likely that there is an EEPROM on either J840 or J497 where the batterty capacity is encoded?
OBD11 allows EEPROM access with the 'pro' or 'ultimate' versions, but I'm not going to mess with that on a complete vehicle - only on disassembled modules. I'm looking at EEPROM readers/programmers, maybe something custom built on Arduino?

Anyhow simple change the Cells and see what happens.

You are absolutely right. And this is my preferred approach to projects.
Once I have my e-Golf, a spare battery pack and some new cells then we shall see what the car thinks of its higher capacity.

[SuperV8]

Interesting project. I can't help regarding battery upgrade - but I am familiar with other VAG upgrades.
For example - when fitting a larger brake system 288 to 312mm - you can/should code the car for the new brake size so the ABS/TSC 'knows' the brake system and will adjust it's parameters to suit. This only works where an alternate brake system was offered - so you wouldn't be able to code it for an RS4 brake system as this was never offered on the Golf for example.
Would be nice if you could simply code the car to the 35.8kWh pack.

[jrbe]

I won't be of much help besides linking to some work that may be of interest or could help with what you're trying to do. In the event that you just can't code the increased capacity in coding / basic settings / adaptations here's some info on going the deep route.

The effort in this link is for editing some parameters in an electric power steering module code, but would likely be a similar effort to do to a bms and maybe the vehicle control unit to change the battery size.
https://icanhack.nl/blog/vw-part1/

[dnoermann]

The link you posted has some interesting info:

Address 8C: Hybrid Battery (J840) Labels: None
Part No SW: 5GE 915 225 B HW: 5GE 915 225 B
Component: K8C 005 0400
Serial number: 03012001013888
Coding: 000000000000000000000000000000000000000000000000000000000000
Shop #: WSC 00000 000 00000
ASAM Dataset: EV_BECM08820215GE915225B 001004
ROD: EV_BECM08820215GE915225B.rod
VCID: 3B2331C623E69683460-806E

Perhaps one of the numbers in there is interpreted as the installed capacity?

Coding can change Configurations, but as you see coding is all 0 so coding is not used in this Unit.
The Dataset is the thing that we wont to change.
You only see the VW Internal Dataset Name that was used, not the Data.
As said Dataset is in XML Format, but in Unit its Really Binary Data that is saved Via Can UDS Protocoll.
Dataset can probably read out from ECU. VCDS can´t do it.
Odis Engeneering or VCP is your Tool for that.
I will add the Read/Write Feature for Dataset in my python scrips https://github.com/dnoermann/car-tools as soon as i find time.
With Online Workshop Access you can request newest Dataset from VW Servers and save it at right moment of transfer, thats how most Datasets are beeing found ....

[dnoermann]

With your knowledge on reverse engineering of ECUs, is it likely that there is an EEPROM on either J840 or J497 where the batterty capacity is encoded?

Yes, 90% Chance its a simple external eeprom on pcba.
10% Chance its internal one in the CPU used

[ronmcmahon]

I have a 2018 e-Golf and am researching battery capacity expansion.
It has been many months since the last update to this conversation - any progress?